The Occoquan River flows into the Potomac River at Belmont Bay, and is located in Northern Virginia, along the mid-Atlantic coast of the United States (USA). The river is approximately 20 mi (32 km) long and its watershed covers about 590 square miles (1,528.09 km²). It is formed by the confluence of Broad Run and Cedar Run, in Prince William County; Bull Run enters it ESE of Manassas, as it turns to the southeast. It is part of the Chesapeake Bay watershed.
While also viewed as a scenic area, many local high schools and colleges use the river for sport rowing.
The Occoquan has three dams along its length. The first is at the Town of Occoquan, a reservoir belonging to the Fairfax County Water Authority that serves as a source of drinking water for parts of Fairfax and Prince William Counties, Virginia. The Occoquan Reservoir stretches from Occoquan to Bull Run. Further upriver is Lake Jackson. The dam that creates Lake Jackson is at Virginia Route 234, Dumfries Road, and is a former hydroelectric facility. Today the dam contains the lake, but has not produced electricity in several decades.
There is a third dam up Broad Run from its confluence with Cedar Run; this dam forms Lake Manassas, which is the primary water supply for the City of Manassas.